In wellbore drilling and completion, various tubular elements (also typically referred to in the industry as “tubulars”) need to be connected to each other. For example, in well completions, a number of tubulars may have to be connected end to end in order to form a string of tubulars such as a casing string or liner string to line the wellbore to the required depth. In some cases, one tubular has to be set inside another tubular by increasing the diameter of the inner tubular until it contacts the inner wall of the outer tubular and creates an interference fit therewith. The connection between the tubulars very often must be capable of withstanding axial loads (i.e. secured). The connection should also be fluid tight to provide an annular barrier between the tubulars (i.e. sealed) to prevent fluid passage between the internal bore of the outer tubular and the exterior of the inner tubular.
One prior art arrangement for connecting tubular members in a wellbore is described in WO2011/048426 A2 and includes a metal to metal seal between first and second tubular members 1, 2 in a cased wellbore, as shown in FIGS. 1 and 2 of the present application. The second (lower) tubular member 2 includes an upper end portion 21 which has a greater inner diameter than the outer diameter of a lower end portion 11 of the first (upper) tubular member 1. Circumferential recesses or grooves 22 are formed on the inner surface or bore of the upper end portion 21 of the second (lower) tubular member 2. In order to form the seal, firstly, the lower end portion 11 of the first tubular member 1 is located within the upper end portion 21 of the second tubular member 2. Next, a hydraulic expansion tool 3 is lowered from surface inside the first tubular member 1 to the intended location of the seal (see FIG. 2 of the present application). The tool 3 seals off a chamber 7 between a pair of axially spaced apart seals 8. Actuation of the hydraulic expansion tool 3 causes chamber 7 to be filled with fluid under high pressure, and this high pressure fluid acts on the inner surface or bore of the lower end portion 11 of the first tubular member 1 to first elastically and then plastically expand so that the lower end portion 11 expands radially outwardly along a length bounded by the seals 8 into the recesses 22 on the inner bore of the second tubular member 2 such that circumferential protrusions 12 or ridges are formed on the outside of the lower end portion 11 of the first tubular portion 1. These protrusions 12 are received in the recesses 22 until a seal is formed between the first and second tubular members 1, 2.
A similar technique is used to connect an overshot device with a tubular downhole, e.g. casing or liner, in fishing operations, to engage an inner bore surface of the overshot device with the outer surface of the tubular, to allow jarring and retrieval of the tubular.
The problem associated with the above described arrangement is that well fluid present at the interface between the tubular members may become trapped in the recesses which can lead to the formation of hydraulic lock which is potentially damaging to the tubular members and/or means that an effective seal is not formed. In order to exclude fluid, a crushable medium, such as, for example, syntactic foam is sometimes placed into the recesses. In order to place the crushable medium, such as syntactic foam into the recesses, it is necessary to form rings formed from the crushable material which must conform precisely to the shape of the recess. In addition, the circumferential recesses or grooves (into which the crushable rings are inserted) must be preformed or machined and set in the wellbore at a suitable depth prior to any connection being made.
Both manufacturing of the crushable rings and machining of the grooves are difficult and costly and extremely difficult to achieve in tubing having an internal diameter less than 7″ (17.5 cm) and, furthermore, it is very difficult to remove the crushable rings if that is required for any reason.
Another type of connection, which addresses the problem of fluid exclusion, is described in EP2013445 B1 and illustrated in FIG. 3 of this present application. In EP2013445 B1, a first (inner) tubular member 4 is expanded into a second (outer) tubular member 5 using the same expansion tool 3 as in FIGS. 1 and 2 which seals off a chamber 7 with axially spaced apart seals 8. The first tubular member 4 has an expandable portion 40 which has a central section 41 and end regions 42. The wall thickness of the central section 41 is relatively uniform and is thinner than the wall thickness of the end regions 42. Tapered portions 43 provide transitional regions between the thinner wall of the central section 41 and the thicker end regions 42. When the tool 3 is actuated, the central section 41 expands prior to the end regions 42 due to the former's thinner sidewall thickness, thereby driving any fluid at the annular interface between the outer surface of the first and the inner surface of the second tubular members 4, 5 in opposite directions axially beyond the end regions 42 into the annular space 9. Seals 6 at the end regions 42 on the outside of the first tubular member 4 provide an additional fluid barrier between the tubular members 4, 5 when the expandable portion 40 has been fully expanded. Since the seals 6 make contact with the second tubular member 5 only after the fluid has been expelled from the interface between the tubular members 4, 5, the occurrence of a hydraulic lock is avoided.
The arrangement of EP2013445B1 suffers from the same drawback as the tubular connection of WO2011/048426 A2 that the tubular members between which the seal connection is made have relatively complicated profiles, particularly the first (inner) tubular member 4 due to its varying sidewall thickness, which results in relatively high manufacturing costs. In addition, the performance of such a connection is limited due to the limited means of modifying the single piece assembly.
Accordingly, the object of the present invention is to provide an expandable tubular connection which is relatively inexpensive to manufacture whilst being capable of providing a reliable hermetic seal and/or being capable of creating a secure connection through which axial force can be transferred and therefore resist relative axial movement occurring. In addition, the object of the present invention is to provide an expandable tubular connection which can be readily adapted to suit different applications.